Stick your head up under the dash and look for rust, in the corners. my first sedan had big holes on both sides here, its not seen from the engine bay, and i never noticed until water started dripping on my knee while driving. Also floor pans.

Also look for accident damage, look very close at where the guards bolt up under the bonnet, close to the headlight. Pop your head under the front end and look for cracks where the radius rods mount to the chassis, and any evidence of repairs. Im a spraypainter and any car that 40 or so years old would have been in a smash repairs at some point in its life.